A soil such as potting soils or regular earth should have the following characteristics for good plant growth:
1. Provide adequate support for growing plants by holding roots firmly in place yet permitting good root penetration from new growth.
2. Hold moisture and nutritional elements in forms and locations where they are easily assimilated by plants.
3. Permit oxygen or general aeration in the root zones to prevent bacterial attack and decay from overwatering.
4. Provide good drainage.
5. Be free of harmful insects, or disease-causing bacteria that are harmful to plants.
To obtain these characteristics, the soil should have internal porosity, be resistant to compaction, have a pH in the range of 6.4 to 7.2, and be free of pathogens and insects.
Most naturally occurring soils do not have all of the foregoing characteristics. Synthetic soils, commonly referred to as potting soils, have been used extensively in the horticultural industry and, properly designed, are actually superior to naturally-occurring soils as a growing medium. U.S. Pat. No. 3,932,166, proposes adding charred wood, sawdust, straw, cardboard, cane baggase, oat hulls, cotton gin wastes, animal manures, bark and paper as soil conditioners, among other uses. These materials are of low porosity and they readily compact. While a variety of potting soils have been proposed and used in the horticultural industry, these soils do not have all of the foregoing characteristics, and it is necessary to include chemicals to adjust the pH of the soil to obtain maximum growth. Accordingly, it would be highly desirable to provide potting soils and naturally-occurring soils with the foregoing characteristics and, at the same time, be able to selectively modify such characteristics.